International Publication No. WO 2014/131479 A1 discloses an inking system for inking an intaglio printing cylinder of an intaglio printing press, which intaglio printing cylinder carries one or more intaglio printing mediums, the inking system comprising an ink collecting cylinder designed to cooperate with the intaglio printing cylinder and to collect ink patterns from a plurality of inking devices that are distributed about a portion of the circumference of the ink collecting cylinder, wherein at least one of the inking devices, preferably each inking device, comprises a selective inking cylinder cooperating with the ink collecting cylinder, wherein the selective inking plate comprises a coating that is selectively structured to exhibit ink-repellent portions and perform selective transfer of ink at locations corresponding to engraved areas of the one or more intaglio printing mediums that are to be inked with the ink supplied by the associated inking unit.
Publication U.S. Pat. No. 4,516,496 A discloses an inking system for inking an intaglio printing cylinder, comprising an ink collecting cylinder designed to collect ink patterns from a plurality of inking devices each having a selective inking cylinder that are distributed about a portion of the circumference of the ink collecting cylinder.
Furthermore, intaglio printing presses are already known in the art, for instance from Swiss Patent No. CH 685 380 A5, European Patent Publications Nos. EP 0 406 157 A1, EP 0 415 881 A2, EP 0 563 007 A1, EP 0 873 866 A1, and International Publications Nos. WO 03/047862 A1, WO 2005/077656 A1, WO 2008/146193 A1, WO 2011/077348 A1, WO 2011/077350 A1, WO 2011/077351 A1, WO 2013/153519 A2, all assigned to the instant Applicant.
In the above-listed intaglio printing presses, inking of the plate cylinder carrying the intaglio printing plate(s) (which plate cylinder acts as intaglio printing cylinder) is typically carried out by means of a plurality of inking devices that cooperate either directly with the plate cylinder or indirectly, via an ink collecting cylinder (also referred to in the art as “Orlof” cylinder) that collects ink from multiple inking devices. Each such inking devices comprises a chablon cylinder that cooperates either with the plate cylinder or the ink collecting cylinder (if present), which chablon cylinder carries a chablon plate comprising relief portions corresponding to engraved areas of the intaglio printing plates that are to be inked with a given ink supplied by an associated inking unit placed upstream of the chablon cylinder.
FIGS. 1a and 1b schematically illustrate a known intaglio printing press as for instance disclosed in International Publication No. WO 2013/153519 A2, which printing press is generally designated by reference numeral 1.
More precisely, FIG. 1a shows a sheet-fed intaglio printing press 1 comprising a sheet feeder 2 for feeding sheets to be printed, an intaglio printing unit 3 for printing the sheets, and a sheet delivery unit 4 for collecting the freshly-printed sheets. The intaglio printing unit 3 includes an impression cylinder 7, a plate cylinder 8 acting as intaglio printing cylinder (in this example, the plate cylinder 8 is a three-segment plate cylinder carrying three intaglio printing plates 8a, 8b, 8c ), an inking system comprising an ink collecting cylinder, or Orlof cylinder, 9 (here a three-segment blanket cylinder carrying a corresponding number of blankets) for inking the surface of the intaglio printing plates 8a, 8b, 8c carried by the plate cylinder 8 and an ink wiping system 10 for wiping the inked surface of the intaglio printing plates 8a, 8b, 8c carried by the plate cylinder 8 prior to printing of the sheets.
The sheets are fed from the sheet feeder 2 onto a feeder table and then onto the impression cylinder 7. The sheets are then carried by the impression cylinder 7 to the printing nip between the impression cylinder 7 and the plate cylinder 8 where intaglio printing is performed. Once printed, the sheets are transferred away from the impression cylinder 7 for conveyance by a sheet transporting system 11 in order to be delivered to the delivery unit 4. The sheet transporting system 11 conventionally comprises a sheet conveyor system with a pair of endless chains driving a plurality of spaced-apart gripper bars for holding a leading edge of the sheets (the freshly-printed side of the sheets being oriented downwards on their way to the delivery unit 4), sheets being transferred in succession to a corresponding one of the gripper bars.
During their transport to the sheet delivery unit 4, the freshly printed sheets are preferably inspected by an optical inspection system 5. In the illustrated example, the optical inspection system 5 is advantageously an inspection system as disclosed in International Publication No. WO 2011/161656 A1 (which publication is incorporated herein by reference in its entirety), which inspection system 5 comprises a transfer mechanism and an inspection drum located at the transfer section between the impression cylinder 7 and chain wheels of the sheet transporting system 11. The optical inspection system 5 could alternatively be an inspection system placed along the path of the sheet transporting system 11 as described in International Publications Nos. WO 97/36813 A1, WO 97/37329 A1, and WO 03/070465 A1. Such inspection systems are in particular marketed by the Applicant under the product designation NotaSave®.
Before delivery, the printed sheets are preferably transported in front of a drying or curing unit 6 disposed after the inspection system 5 along the transport path of the sheet transporting system 11. Drying or curing could possibly be performed prior to the optical inspection of the sheets.
FIG. 1b is a schematic view of the intaglio printing unit 3 of the intaglio printing press 1 of FIG. 1a. As already mentioned, the intaglio printing unit 3 basically includes the impression cylinder 7, the plate cylinder 8 with its intaglio printing plates 8a, 8b, 8c, the inking system with its ink collecting cylinder 9, and the ink wiping system 10.
The inking system comprises in this example five inking devices 90, all of which cooperate with the ink collecting cylinder 9 that contacts the plate cylinder 8. It will be understood that the illustrated inking system is adapted for indirect inking of the plate cylinder 8, i.e. inking of the intaglio printing plates 8a, 8b, 8c via the ink collecting cylinder 9. The inking devices 90 each include an ink duct comprising a duct roller 91 cooperating in this example with a pair of ink application rollers 92. Each pair of ink application rollers 92 in turn inks a corresponding chablon cylinder 93 which is in contact with the ink collecting cylinder 9. As is usual in the art, each chablon cylinder 93 carries a chablon plate 93a (also referred to as a “poly-chablon plate” or “stencil plate”) that is structured so as to exhibit relief portions 93A corresponding to the areas of the intaglio printing plates 8a, 8b, 8c intended to receive the inks in the corresponding colours supplied by the respective inking units 91/92 (see also the photographic illustration of FIG. 2). In essence, each chablon plate 93a is functionally equivalent to a letterpress plate, with the relief portions 93A acting as ink transfer portions.
As shown in FIGS. 1a, 1b and 2, the impression cylinder 7 and plate cylinder 8 are both supported in a stationary (main) frame 50 of the printing press 1. The inking devices 90 (including the duct roller 91 and ink application rollers 92) are supported in a mobile inking carriage 52, while the ink collecting cylinder 9 and chablon cylinders 93 are supported in an intermediate carriage 51 located between the inking carriage 52 and the stationary frame 50. Both the inking carriage 51 and the intermediate carriage 52 are advantageously suspended under supporting rails. In that respect, the photographic illustration of FIG. 2 shows three of the chablon cylinders 93 mounted in the intermediate carriage 51, with the inking carriage 52 (not visible in FIG. 2) being moved to a retracted position (as schematically illustrated by dashed lines in FIG. 1a).
The ink wiping system 10, on the other hand, typically comprises a wiping tank, a wiping roller assembly supported on and partly located in the wiping tank and contacting the plate cylinder 8, cleaning means for removing wiped ink residues from the surface of the wiping roller assembly using a wiping solution that is sprayed or otherwise applied onto the surface of the wiping roller assembly, and a drying blade contacting the surface of the wiping roller assembly for removing wiping solution residues from the surface of the wiping roller assembly. A particularly suitable solution for the ink wiping system 10 is disclosed in International Publications Nos. WO 2007/116353 A1 and WO 2013/132471 A1, which publications are incorporated herein by reference in their entirety.
A limitation with the known inking system that make use of chablon cylinders, as for instance illustrated in FIGS. 1a, 1b and 2, resides in the fact that the chablon plates 93a typically comprise an outer layer acting as ink transfer layer, which is made of a relatively soft and resilient material (such as a light sensitive photopolymer layer bonded to a steel base plate) that is structured to form the relief portions 93A that cover the relevant areas of the intaglio printing plates to be inked with the desired ink. Such chablon plates 93a are for instance marketed by company Flint Group under the product designation nyloprint® (in particular nyloprint® WS 230 S or WS 230 Digital stencil plates) and are typically structured by exposure through a laser-ablatable mask (LAM) layer that has been removed (namely ablated by laser) in the portions that are to remain as the desired relief portions 93A after exposure to light and subsequent washing of the unexposed photopolymer layer. The resulting relief portions 93A are typically rather simple and basically exhibit a continuous surface where ink is to be transferred as illustrated for instance in the photographic illustration of FIG. 2. Due to the relatively soft and resilient nature of the material forming the relief portions 93A, it is typically not possible to structure the relief portions 93A of the chablon plates 93a so as to exhibit very fine structures. The resolution of the chablon plates is therefore limited and the relief portions 93A typically restricted to rather crudely-defined surfaces that only vaguely reflect the engraved areas to be inked on the intaglio printing plates.
This further implies that the amount of ink that is transferred by each chablon cylinder is relatively substantial, which leads to a high consumption of ink as all excess ink that is deposited outside of the engraved areas of the intaglio printing plates is wiped off by the wiping system and ends up as waste.
Solutions have been proposed to reduce the consumption of ink by compensating the elongation of the intaglio printing plates, thereby allowing the use of chablon plates with smaller relief portions that more precisely match the engraved areas of the intaglio printing plates to be inked (see e.g. International Publications Nos. WO 2004/069538 A2 and WO 2013/160853 A2), but improvements are still required and welcome.
British Patent No. GB 987,102 discloses an old concept of an intaglio printing press where the plate cylinder acting as intaglio printing cylinder is inked by means of multiple inking devices, each comprising an ink fountain supplying ink to a duct roller, which transfers the ink to an inking roller cooperating with the plate cylinder via an intermediate transfer roller and a so-called “partial-image cylinder” which rotates in contact with the intermediate ink transfer roller and the inking roller. In contrast to the previously mentioned solutions, the inking roller (which likewise consists of or is coated with a resilient material) is solid and has a continuous surface, i.e. does not exhibit any relief portion, whereas the partial-image cylinder is made of a hard (e.g. metallic) material that is structured to exhibit relief portions precisely matching the delineation of the engraved areas of the intaglio printing plates that are to be inked in the relevant ink.
By way of alternative, GB 987,102 also contemplates to employ ink-repelling means of the type used for lithographic printing processes as a way to carry out the selective transfer of ink by means of the partial-image cylinder.
A problem with the solution disclosed in British Patent No. GB 987,102 however resides in the fact that the inking rollers are in continuous rolling contact with the plate cylinder and therefore take up ink deposited by the other inking devices, potentially leading to ink contamination and print quality issues.
An improved solution is thus required.